Mesencephalic astrocyte-derived neurotropic factor is an important factor in chondrocyte ER homeostasis

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) resident protein that can be secreted due to an imperfect KDEL motif. MANF plays a cytoprotective role in several soft tissues and is upregulated in conditions resulting from intracellular retention of mutant protein, including two skeletal diseases, metaphyseal chondrodysplasia, Schmid type (MCDS) and multiple epiphyseal dysplasia (MED). The role of MANF in skeletal tissue homeostasis is currently unknown. Interestingly, cartilage-specific deletion of Manf in a mouse model of MED resulted in increased disease severity, suggesting its upregulation may be chondroprotective. Treatment of MED chondrocytes with exogenous MANF led to a decrease in the cellular levels of BiP (GRP78), confirming MANF's potential to modulate ER stress responses. However, it did not alleviate the intracellular retention of mutant matrilin-3, suggesting that it is the intracellular MANF that is of importance in the pathobiology of skeletal dysplasias. The Col2Cre-driven deletion of Manf from mouse cartilage resulted in a chondrodysplasia-like phenotype. Interestingly, ablation of MANF in cartilage did not have extracellular consequences but led to an upregulation of several ER-resident chaperones including BiP. This apparent induction of ER stress in turn led to dysregulated chondrocyte apoptosis and decreased proliferation, resulting in reduced long bone growth. We have previously shown that ER stress is an underlying disease mechanism for several skeletal dysplasias. The cartilage-specific deletion of Manf described in this study phenocopies our previously published chondrodysplasia models, further confirming that ER stress itself is sufficient to disrupt skeletal growth and thus represents a potential therapeutic target.

Cartilage-specific ablation of XBP1 signaling in mouse results in a chondrodysplasia characterized by reduced chondrocyte proliferation and delayed cartilage maturation and mineralization

OBJECTIVE

To investigate the in vivo role of the IRE1/XBP1 unfolded protein response (UPR) signaling pathway in cartilage.

DESIGN

Xbp1(flox/flox).Col2a1-Cre mice (Xbp1(CartΔEx2)), in which XBP1 activity is ablated specifically from cartilage, were analyzed histomorphometrically by Alizarin red/Alcian blue skeletal preparations and X-rays to examine overall bone growth, histological stains to measure growth plate zone length, chondrocyte organization, and mineralization, and immunofluorescence for collagen II, collagen X, and IHH. Bromodeoxyuridine (BrdU) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analyses were used to measure chondrocyte proliferation and cell death, respectively. Chondrocyte cultures and microdissected growth plate zones were analyzed for expression profiling of chondrocyte proliferation or endoplasmic reticulum (ER) stress markers by Quantitative PCR (qPCR), and of Xbp1 mRNA splicing by RT-PCR to monitor IRE1 activation.

RESULTS

Xbp1(CartΔEx2) displayed a chondrodysplasia involving dysregulated chondrocyte proliferation, growth plate hypertrophic zone shortening, and IRE1 hyperactivation in chondrocytes. Deposition of collagens II and X in the Xbp1(CartΔEx2) growth plate cartilage indicated that XBP1 is not required for matrix protein deposition or chondrocyte hypertrophy. Analyses of mid-gestation long bones revealed delayed ossification in Xbp1(CartΔEx2) embryos. The rate of chondrocyte cell death was not significantly altered, and only minimal alterations in the expression of key markers of chondrocyte proliferation were observed in the Xbp1(CartΔEx2) growth plate. IRE1 hyperactivation occurred in Xbp1(CartΔEx2) chondrocytes but was not sufficient to induce regulated IRE1-dependent decay (RIDD) or a classical UPR.

CONCLUSION

Our work suggests roles for XBP1 in regulating chondrocyte proliferation and the timing of mineralization during endochondral ossification, findings which have implications for both skeletal development and disease.

Acrylamide and 2,5-hexanedione induce collapse of neurofilaments in SH-SY5Y human neuroblastoma cells to form perikaryal inclusion bodies

Neurofilament accumulations are characteristic of a number of neurological conditions including amyotrophic lateral sclerosis, giant axonal neuropathies and several chemically-induced neuropathies. Although the mechanism(s) leading to neurofilament accumulation are unknown, it is possible that similar processes occur both in disease and in chemically-induced neuropathies. Understanding the mechanism(s) of chemically-induced neurofilament accumulation, which is more amenable to experimental manipulation, may give insight into the neurological diseases they mimic. We have compared the effects of two chemically-dissimilar neurotoxins, 2,5-hexanedione and acrylamide, on neurofilaments in the human neuroblastoma cell line, SH-SY5Y. Both undifferentiated and differentiated SH-SY5Y cells were exposed to 2,5-hexanedione or acrylamide and changes in cytoskeletal organization examined by immunofluorescence and electron microscopy. Although distinct morphological differences have previously been characterized in the neuropathies induced by 2,5-hexanedione and acrylamide in vivo, we have found that both compounds had similar direct effects on neurofilaments in SH-SY5Y cells, inducing formation of perikaryal inclusion bodies. In addition, differentiated SH-SY5Y cells were more sensitive to both 2,5-hexanedione and acrylamide compared with undifferentiated cells. These similar effects of 2,5-hexanedione and acrylamide lend further support that a common mechanism(s) may lead to neurofilament accumulation in these neuropathies. SH-SY5Y cells provide a useful model to investigate further the biochemical basis of neurofilament accumulation.

Phosphorylation of tau by glycogen synthase kinase-3 beta in intact mammalian cells: the effects on the organization and stability of microtubules

The phosphorylation state of tau changes during neurodevelopment and highly phosphorylated tau accumulates in the paired helical filaments found in Alzheimer's disease. In non-neuronal mammalian cells transiently expressed tau is predominantly not phosphorylated at sites known to be phosphorylated in paired helical filaments. However this pattern of phosphorylation is induced by both glycogen synthase kinase-3 alpha and -3 beta and here we show that this results in a change in the intracellular properties of tau. Within cells tau is bound to cytoskeletal structures and causes changes in cellular cytoarchitecture with the induction of thick and stable microtubule bundles. This morphology is lost when tau is co-expressed with glycogen synthase kinase-3 beta; microtubules become less stable and are not bound by tau. Independently of any direct or indirect effects on tau, glycogen synthase kinase-3 beta induces some but relatively slight changes in microtubule organization with the loss of a prominent centrosomal microtubular origin. The cytoskeleton is critical to cell function and within post-mitotic neurons has a highly specialized structure induced, in part, by the neuronal-specific microtubule-associated proteins such as tau. In vitro studies have suggested that the properties of tau are regulated by phosphorylation as highly phosphorylated tau does not promote tubulin polymer assembly. We have demonstrated, in intact cells, that tau highly phosphorylated in the presence of glycogen synthase kinase-3 beta loses the properties of microtubule binding and stabilization, suggesting that regulation of tau phosphorylation by this enzyme might be an important mechanism whereby cytoskeletal function is modulated during neurodevelopment and lost in neurodegeneration.

In vitro attachment to a human cell line of Escherichia coli strains causing urinary-tract infection: occurrence of fimbriae (pili) in adhesive and non-adhesive strains

In this study, 20 strains of Escherichia coli isolated from infected urinary-tract were screened for the occurrence of haemagglutinating (HA) activity and for the possible relationship between a fimbriate surface structure and adhesion ability to the surface of a human cell line. Only 8 of the 20 adhesive strains agglutinated human or guinea-pig erythrocytes or both. In 7 of the 8 strains, the haemagglutinating activity with human erythrocytes was D-mannose-resistant; one strain was D-mannose-sensitive with guinea-pig red blood cells (RBC). In 40 non-adhering E. coli isolated from urine, D-mannose-resistant HA was rarely detected; in contrast, agglutination of guinea-pig was more frequent and D-mannose-sensitive when it occurred. No correlation was found between the degree of HA activity and the ability to adhere. Moreover at low growth temperature (18 degrees c), haemagglutinin was absent in all the strains tested, whereas residual adhesion capacity could be detected in some strains. Similar results were recorded after heating the bacterial suspension at 65 degrees C. Generally pili detected by electron microscopy were present at the surface of the strains which agglutinated RBC. There is no correlation between the presence of fimbriae or pili and adhesion of E. coli to the human cell line used in this study. A range of distinct mechanisms of E. coli adhesion appeared to be involved in the phenomenon described in this report.

Adhesion to a human cell line by Escherichia coli strains isolated during urinary tract infections

It has been shown that some, but not all, Escherichia coli strains isolated from urine adhere, in vitro, to the surface of uroepithelial or vaginal cells. In the present study, 212 strains, isolated from urine of 212 infected patients, were tested for adhesion by using an in vitro human cell line assay. A variable degree of attachment to the cell monolayer was detected in these strains. From patients with cystitis, only 19 (9.7%) of the 195 strains examined were adherent, whereas 5 (29.4%) of the 17 pyelonephritis strains had similar properties (P less than 0.05). To investigate the incidence of adhesion in the clinical manifestations of urinary tract infection, a sample of patients was picked at random from those with cystitis. During cystitis caused by adhesive bacteria, patients suffer more often from macroscopic hematuria than from dysuria, frequency, or recurrency (P less than 0.05). This study shows that E. coli strains isolated from urine samples possess a strikingly difference in capacity to adhere to a human cell line surface as demonstrated previously with uroepithelial or vaginal cells. Moreover, according to these data, the adhesion of E. coli may be considered as a virulent factor and would play a part in the infection of the urinary tract in humans.

Adhesion of commensal bacteria to the large intestine wall in humans

Biopsies taken during colonoscopic examination of the human large bowel were used to examine the relationship of the commensal bacterial to the mucosal epithelial cell surface. Bacteria were seen adhering to the exposed epithelial cell surface and also to the mucus sheet. Isolation of aerobic organisms showed that Escherichia coli are closely associated with the gut wall throughout the large intestine. One strain of E. coli predominated in each biopsy, and this strain was present along the whole length of bowel. Adhesion of bacteria to the gut wall does occur in vivo and may be one of the factors involved in the ability of an organism to colonize and persist.

Effects of cephalexin, erythromycin and clindamycin on the aerobic Gram-negative faecal flora in man

The effects of 5-day courses of orally administered cephalexin, clindamycin and erythromycin on the Gram-negative, aerobic faecal flora of healthy adults were examined. The concentration of cephalexin reached in the intestine was high enough to cause the emergence of resistant Gram-negative bacteria; organisms belonging to the genera Enterobacter, Citrobacter and Pseudomonas increased to easily detectable levels. The faecal concentration of erythromycin was high and caused a severe reduction of the coliform flora. Clindamycin administration resulted in a considerable increase in the coliform count; the increase in the proportion of klebsiellae was especially marked.

Antibiotic resistance and survival of E coli in the alimentary tract

Some antibiotics tend to select for R-factor-carrying Escherichia coli in the human gut, with complex long-term consequences. Some resistant strains disappear rapidly when treatment ends, while others persist for months in the absence of obvious antibiotic selection pressure, and the performance of individual resistant strains seems to depend more on the nature of the strain than on the plasmid carried. R plasmids are relatively rare in those E coli that colonize well in the gut and resistant bacteria therefore tend to disappear when treatment ends, but this situation could change dramatically if R plasmids became prevalent among those strains of E coli that colonize effectively.

Distribution of R plasmids among the O-antigen types of Escherichia coli isolated from human and animal sources

The O-antigen types of 600 independently isolated Escherichia coli strains from human feces have been determined, and the types have been related to the antibiotic resistance patterns of the strains. The relative abundance of each O-antigen type differed in the susceptible and resistant series of strains. The majority (86%) of the resistant strains carried R plasmids. Resistant E. coli (20.3%) were found associated with O-antigen types 8, 9 and 101, whereas the susceptible strains covered a wide range of O-antigen types. Examination of 174 resistant strains isolated from calf feces also showed a prevalence of O-antigen types 8, 9, 101 (24.1%), and it seems probable that strains expressing these three O-antigen types commonly carry R plasmids in the alimentary tracts of man and calves. The number of strains not typeable with the O sera available were similar in the human (12.5%) and the calf (11.5%) series. There are no grounds for distinguishing "human" from "calf" E. coli on the basis of their O-antigen reactions.